Silica glass with saturated induced absorption and method of making

Abstract

A silica glass article, such as a lens in a stepper/scanner system, having saturated induced absorption at wavelengths of less than about 250 nm. Saturated induced absorption is achieved by first removing Si—O defects in the silica glass by forming silicon hydride (SiH) at such defects, and loading the silica glass with hydrogen to react with E′ centers formed by photolysis of SiH in the silica glass article. The silicon hydride is formed by loading the silica glass with molecular hydrogen at temperatures of at least 475° C. After formation of SiH, the silica glass is loaded with additional molecular hydrogen at temperatures of less than 475° C.

1. A method of making a silica glass article, the silica glass article having a saturated induced absorption, the method comprising the steps of:
 a. providing a silica glass article, the silica glass article having a plurality of Si—O defects that form E′ centers when exposed to ultraviolet radiation having a wavelength of less than about 250 nm; 
 b. providing molecular hydrogen to remove at least a portion of the plurality of Si—O defects by forming SiH at each of the Si—O defects in the silica glass article; and 
 c. providing molecular hydrogen to react with E′ centers formed by photolysis of SiH in the silica glass article before exposing the silica glass article to ultraviolet or deep ultraviolet radiation, wherein the silica glass article has a saturated induced absorption at wavelengths of less than about 250 nm when exposed to ultraviolet radiation having a wavelength of less than about 250 nm. 
 
     
     
       2. The method according to  claim 1 , wherein the silica glass article has a saturated induced absorption of less than about 0.01/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       3. The method according to  claim 2 , wherein the saturated induced absorption is less than about 0.005/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       4. The method according to  claim 3 , wherein the saturated induced absorption is less than about 0.002/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       5. The method according to  claim 1 , wherein the step of forming SiH at the Si—O defects comprises a first loading step, the first loading step comprising heating the silica glass article at a first temperature of at least about 475° C. in a hydrogen-containing atmosphere. 
     
     
       6. The method according to  claim 5 , wherein the first temperature is in a range from about 475° C. up to about 1000° C. 
     
     
       7. The method according to  claim 5 , wherein the silica glass article has a SiH concentration after the first loading step in a range from about 1×10 14  SiH species/cm 3  up to about 2×10 16  SiH species/cm 3 . 
     
     
       8. The method according to  claim 1 , wherein the step of providing molecular hydrogen to react with E′ centers formed by photolysis of SiH in the silica glass article comprises a second loading step, the second loading step comprising loading the silica glass article with molecular hydrogen. 
     
     
       9. The method according to  claim 8 , wherein the second loading step comprises heating the silica glass article at a second temperature of less than about 475° C. in a hydrogen-containing atmosphere. 
     
     
       10. The method according to  claim 9 , wherein the second temperature is less than about 475° C. and greater than or equal to about 300° C. 
     
     
       11. The method according to  claim 8 , wherein the second loading step comprises loading the silica glass article with molecular hydrogen to a concentration of at least 1×10 16  H 2  molecules/cm 3 . 
     
     
       12. The method according to  claim 11 , wherein the concentration of molecular hydrogen is less than about 2×10 18  H 2  molecules/cm 3 . 
     
     
       13. The method according to  claim 1 , wherein induced absorption of the E′ centers produced by SiH photolysis reaches a steady state value and saturates the induced absorption of the silica glass article at less than about 0.01/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       14. A method of making a silica glass article, the silica glass article having a saturated induced absorption, the method comprising the steps of:
 a. providing a silica glass article; 
 b. loading the silica glass article at a first temperature with molecular hydrogen to form SiH, wherein the first temperature is at least about 475° C.; and 
 c. loading the silica glass article with molecular hydrogen at a second temperature after loading at the first temperature and before exposing the silica glass article to ultraviolet or deep ultraviolet radiation, wherein the second temperature is less than about 475° C., to form a silica glass article having a saturated induced absorption at wavelengths of less than about 250 nm when exposed to ultraviolet radiation having a wavelength of less than about 250 nm. 
 
     
     
       15. The method according to  claim 14 , wherein the step of loading the silica glass article with molecular hydrogen at a second temperature comprises providing molecular hydrogen to react with E′ centers formed by photolysis of the SiH in the silica glass article. 
     
     
       16. The method according to  claim 15 , wherein induced absorption of the E′ centers produced by photolysis of the SiH reaches a steady state value and saturates the induced absorption at less than about 0.01/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       17. The method according to  claim 14 , wherein the silica glass article has a SiH concentration in a range from about 1×10 14  SiH species/cm 3  up to about 2×10 16  SiH species/cm 3  after loading with molecular hydrogen at the second temperature. 
     
     
       18. The method according to  claim 14 , wherein loading the silica glass article at a first temperature with molecular hydrogen to form SiH comprises removing at least a portion of Si—O defects in the silica glass article. 
     
     
       19. A method of saturating induced absorption within a silica glass article having a plurality of Si—O defects that form E′ centers when exposed to ultraviolet radiation having a wavelength of less than about 250 nm, the method comprising the steps of:
 a. forming SiH at each of the Si—O defects to remove art least a portion of the plurality of Si—O defects in the silica glass article; and 
 b. providing molecular hydrogen to react with E′ centers formed by photolysis of the SiH in the silica glass article when the silica glass article is exposed to ultraviolet radiation having a wavelength of less than about 250 nm, wherein the silica glass article has a saturated induced absorption at wavelengths of less than about 250 nm, wherein the molecular hydrogen is provided before exposing the silica glass article to ultraviolet or deep ultraviolet radiation. 
 
     
     
       20. The method of  claim 19 , wherein the step of forming SiH at each of the Si—O defects to remove art least a portion of the plurality of Si—O defects comprises a first loading step, the first loading step comprising heating the silica glass article at a first temperature of at least about 475° C. in the presence of a hydrogen-containing atmosphere. 
     
     
       21. The method of  claim 18 , wherein the step of providing molecular hydrogen to react with E′ centers formed by photolysis of the SiH in the silica glass article further comprises a second loading step, the second loading step comprising loading molecular hydrogen into the silica glass article by heating the silica glass article at a second temperature of less than about 475° C. in the presence of a hydrogen-containing atmosphere. 
     
     
       22. The method of  claim 18 , wherein the saturated induced absorption is less than about 0.01/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       23. A silica glass article, the silica glass article comprising up to about up to about 2×10 16  SiH species/cm 3  and a concentration of molecular hydrogen of in a range from 7×10 16  H 2  molecules/cm 3  to about 2×10 18  H 2  molecules/cm 3 , wherein the silica glass article, when exposed to ultraviolet radiation having a wavelength of less than about 250 nm, has a saturated induced absorption at wavelengths of less than about 250 nm. 
     
     
       24. The silica glass article of  claim 23 , wherein the saturated induced absorption is less than about 0.01/cm after exposure to 200,000 pulses of 193 nm laser radiation at a fluence of 22 mJ/cm 2 ·pulse. 
     
     
       25. The silica glass article of  claim 23 , wherein the silica glass article is first loaded at a first temperature of at least about 475° C. with molecular hydrogen to form SiH, and then loaded with molecular hydrogen at a second temperature of less than about 475° C. 
     
     
       26. The method of  claim 1 , wherein the saturated induced absorption varies by less than about 5% from a maximum value. 
     
     
       27. The method of  claim 14 , wherein the saturated induced absorption varies by less than about 5% from a maximum value. 
     
     
       28. The method of  claim 14 , wherein the saturated induced absorption varies by less than about 5% from a maximum value.